Heat transfer device



United States Patent Garvin M. McCaskill [72] Inventor Monroeville, Pa.{21] Appl. No. 796,519 [22] Filed Feb. 4, 1969 [45] Patented Dec. 15,1970 [73] Assignee Emerson Electric Co.

St. Loua, Mo.

[54] HEAT TRANSFER DEVICE 7 Claims, 2 Drawing Figs.

[52] US. Cl. 219/530, 219/535. 219/540:138/33.138/112;165/184 [51 1 Int.Cl 1105b 3/06 [50] Field of Search 219/530, 540, 535-537, 301, 365;174/47; 165/1, 183-184, 164, 172; 29/1573; 138/27, 33, 38X, v 1 1 1-1 12[56] References Cited UNITED STATES PATENTS 1,890,784 12/1932 .lacobusassist w13,54s,1ss

Russell et a1 Cohler Brown et a1 Matthews et al.

Snelling... Bilbro FORElGN PATENTS 3/1928 Great Britain 9/1967 GreatBritain Primary Examiner-Velodymyr Y. Mayewsky Attorney-Williams andKreske 219/53OX 165/164X 219/535X 138/111 219/365 219/535 ABSTRACT: Aheat transfer assembly for heat transfer between two conduits which arein peripheral contact, one conduit being adapted to take heat from theother, and a heat transfer material between and in contact withperipheral surfaces of the conduits which are out of contact with eachother. The heat transfer material may be a sheet wound about theconduits or metal foil spirally wound about the conduits,

- v I PATENTED DEB] SIS?!) INVENTOR. GARvm M- McCAsK\LL A TTORNEXS HEATTRANSFER DEVICE BACKGROUND AND SUMMARY There are many applications wheretwo conduits are disposed in peripheral contact so that one takes heatfrom the other. Such peripheral contact limits the surface engagementbetween the conduits substantially to a line along the intercontact andthis limited surface engagement has caused problems. The problems becomemore acute when one of the conduits is an electric heating element,since the limited surface engagement requires the heater to be of a highwattage; otherwise heat transfer would require an undesirable length oftime. Further, since the heat is conducted along a line contact, theheat is not evenly distributed to. the heated conduit and the heater maydevelop hotspots or oxidize to interrupt or impair its operation. 7

It is an object of my invention to improve heat transfer between twoconduits having peripheral intercontact by disposing heat transfermaterial between and in contact with peripheral surfaces of the conduitswhich are out of contact. This enables a lower wattage electric heaterto be used, thereby not only conserving power but also increasingefficiency.

DESCRIPTION OF DRAWING DESCRIPTION or PREFERRED'EMBODIMENT Referring tothe drawing, the heat transfer assembly com- I prises conduits l and 11,110, which are in peripheral intercontact. The diameter of the conduit10 may be large, small or the same as the diameter of the conduits ll,Ila, and contains a substance to be heated. One or more conduits 11maybe used, and in the present embodiment, theconduits are shown aselectric heating elements comprising an elongated metal sheath 12 inwhich is disposed a heating resistor 14 which is electrically insulatedfrom the sheath by highly compacted mineral insulating material 15.

As best seen in FIG. 2, the conduits 11, 11a are disposed longitudinallyof the conduit 10 in peripheral intercontact, and may be held to theconduit in any desired manner, such as by strapping 16 at spaced places.Up to this point, the assembly method is conventional, and it will beappreciated that the conduits have substantially line contact, assumingthat they interengage throughout their coextensive lengths. Such linecontact limits the heat-conducting surface between the conduits and thusseriously impairs efficiency of the heat transfer device.

To improve heat transfer between the conduits 10 and I1, Ila, I proposeto dispose a heat transfer material between and in contact with theperipheral surfaces of the conduits which are out of contact with eachother to additionally transfer heat between the conduits. Such materialmay be in sheet form and wound about the conduits, and it is presentlypreferred to wind a strip of metal foil I7 in spiral fashion about theconduits, as seen in FIG. 2, with adjoining convolutions overlappingslightly. Tape (not shown) may be used to hold the end of the wound foilin place.'The 'foil may be coated on its inside surface with a hightemperature epoxy to restrict galvanic action, or the foil, conduits andstrapping may be formed of compatible metals to restrict such action.

To reduce heat losses, it is preferable to dispose insulating material18 about the foil-enclosed conduits, and such insulation may take anysuitable form, such as preformed halves 19-19 of fiber glass with abacking sheet of aluminum or the like.

As seen in FIG. 1, the foil 17 passes over those portions 20 of theperiphery of the conduits ll, 11a which are opposed to the line ofcontact with the conduit 10, and conduct heat from the sheaths of theheaters 11, 11a through spans 21 to portions 22 of the conduit 10. Itwill be appreciated that the. foil engages the peripheries of theconduits l0 and 11, 11a with more than a line contact because it iswrapped thereabout, and therefore materially assists in even heattransfer from the heaters 11, 11a to the conduit 10.

' I claim: I

l. A heat transfer assembly, comprising a metal tube adapted to containa substance to be heated, an electric heating element having a tubularmetal sheath in peripheral contact with the exterior of said metal tubeto transfer heat from said element to said tube, and an imperforatemetallic banding of good thermal conductivity peripherally aroundencompassing said tube and said sheath and in contact therewith saidbanding comprising a plurality of side-by-side portions each transverseof and in peripheral contact with said tube and said sheath at surfacesthereof which are spaced from their peripheral interengagement, theadjoining margins of said portions being in touching engagement witheach other and in thermal conducting engagement whereby an unbroken heattransfer covering is provided about said tube and said element toadditionally transfer heat therebetween without endangering said heatingelement to development of localized hotspots at portions along itsheating extent.

2. The construction of claim 1 wherein said banding is in the form oflong imperforate metal strip which'is helically wound about tube and thesheath of said heating element, the helical winding disposing adjoiningmargins of adjoining laps in interengagement.

3. The construction of claim 2 wherein said strip is a metal foil, andadjoining margins are in overlapped relation.

4. The construction of claim 1 wherein the inner surface of said bandingis coated with a substance'to restrict galvanic action.

5. The construction of claim 1 wherein said tube, the sheath of saidheating element and said foil are formed of compatible materials whichrestrict galvanic action.

6. The method of improving heat transfer between a metal tube adapted tocontain a substance to adjoining margins of the laps in overlappingrelation. heated, and an electric heating element having a metal sheathin peripheral contact with the exterior surface of said tube to providea first path of good thermal conductivity therebetween, the improvementof providing a second path of good thermal conductivity between saidtube and said sheath without endangering said heating element tolocalized hotspots throughout its heating extent, comprising disposingan imperforate metallic banding of good thermal conductivityperipherally around said tube and sheath and in contact therewith withportions of said banding in sideby-side touching engagement with eachother and in thermal conducting relation with said tube and sheath atsurfaces spaced from their peripheral interengagement, and holdingadjoining margins of said portions in. thermal conducting relation.

7. The method of claim 6 including helically winding said banding aboutsaid tube and sheath with adjoining margins of the laps in overlappingrelation. v

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.548,158 Dated December 15, 1970 lnventofls) Garvin M. McCaskill It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 2 lines 49 and 50 cancel "adjoining margins of the laps inoverlapping relation heated," and insert be heated,

Signed and sealed this 9th day of March 1971 (SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JI Attesting OfficerCommissioner of Patents FORM PO-IOSO (to-6S) uscoMM-Dc 00371

